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Quick Overview

One of the safest ATO’s available. Utilizes an electronic eye sensor to monitor water levels and a backup float switch sensor with audible alarm. A controller protects the quiet metering pump from running dry and reports an empty storage tank. Two magnetic holders for sensors and multiple mounting brackets included.

Easy to use and no need to worry about your tankBy Hamadon 2/28/2015

It saved my time and i do not need to manualy add water. i used it for 200 gallon tank. Thanks BRS

Super ProductBy RDMon 2/20/2015

RDM would recommend this product to a friend

This was easy to setup and get working. I never realized how much I hated having to manually top off my water until I put this in my system. Now I just check my water levels and the fresh water supply and this takes care of adding water as and when it's needed.

EASY and works greatBy Jeffreyon 2/15/2015

Jeffrey would recommend this product to a friend

So far so good ! Have this set up on roughneck bin I'm using to cure my dry rock in. Works perfect and secondary safety offers great piece of mind. In the room one day when pump came on.. manually lifted float and audible alarm sounded and pump shut off. Very comforting to have a piece of equipment like this that is looking out for me ! If you are on the fence, JUST GET IT, you won't be disappointed.

fantastic ATOBy Hawrasseron 2/11/2015

Hawrasser would recommend this product to a friend

this ATO is great. keeps the water level in my sump constant. the only thing i would change is to make the amount of travel on the floating switch a little bit larger. if i turn on my protein skimmer it will sound the alarm but my skimmer is also huge haha

Hoping to get it workingBy Andrewon 1/16/2015

Andrew would recommend this product to a friend

I have had this on an AIO tank (40 gallon) worked great the first week, now it keeps overfilling my tank( alarm going off) in the process of troubleshooting it with Tunze, hope i can get it to work correctly. I wish it worked right out of the box, but based on reviews the Tunze auto top off is suppose to be the best. I have owned other Tunze products before with no problems. Not bashing the auto top off but its not working out of the box. But Tunze customer service is great at helping.

Great ATO! Never missed the target!By Alecon 1/15/2015

Alec would recommend this product to a friend

I don't need to add anymore to those 200+ reviews but I put mine on a timer that only turned on once a day for 10 mins. That way it's not pumping all day long and will never over fill.

Works Great By John Bon 1/10/2015

John B would recommend this product to a friend

Easy set up and I love the optical sensor. My old ATO float valve would often not register the water level depleting and I'd have to refill the sump manually. No issues so far and don't anticipate any. I did have to run the top off line into the tank overflow since my storage container is taller than the sump, but there was plenty of supply hose and I actually like it better.

Best ATO ever By Seadog09 on 1/7/2015

Seadog09 would recommend this product to a friend

The name alone represent quality so you know from start to finish that's what you'll get. I'm happy with my purchase and I know you will be too..

Works flawlessly.By DivingTheWorldon 1/5/2015

DivingTheWorld would recommend this product to a friend

I've had this running for about 4 months now and it works flawlessly. It's really a set it and forget it product. The one quirky thing is that when it first turns on, it will pump water for a few seconds to purge the pump of any air. This is normal and not a but per say, but something to be aware of. I initially had this programmed on my Apex to only turn on a few times a day, but found that it was pumping too much water (due to the starting purge). So now I just leave it on 24 hours a day and it works fine.

Works as promisedBy Jay B.on 1/4/2015

Jay B. would recommend this product to a friend

I bought this to regulate the level in my sump, using RO/DI feed. I also purchased the optional valve. The setup is easy, especially because of the way that the two level sensors are cleverly mounted with the magnetic holder. I turned the water feed on on and everything worked like it was supposed to. Now I don't have to keep fiddling with my protein skimmer to get the right quantity skimmate.

Almost perfectBy Jimon 12/27/2014

Jim would recommend this product to a friend

This is a really great ATO system. There is one downside. If you are pumping the water into your sump, the top level of the top off water container supply cannot be higher than the sump water level. The pump is centrifical, and allows water to flow through the pump when it is off. If the top off water is higher than the sump water, a siphon will occur, and water will continue to flow until the water levels equalize (including over-running the sump, and onto the floor. You simply need to select the right top off container.

ATO's Don't Get Better Than This!By Bernieon 12/20/2014

Bernie would recommend this product to a friend

The Tunze was superior to my first ATO set up which used a float valve and lifter pump. The optical sensor is great and having the second float valve to protect against overfilling is just a smart investment to protect not only your tank but the flooring around it.

I have a controller in which I could probably have set something up myself but for an all in one package this system is great.

I have a litermeter 3 that has failed. It pushes water about 30 feet from the litermeter to a sump tank. Will this pump do the same?

Bulk Reef Supply
Hi Spencer,
The max head pressure on the included pump is about 7ft. It likely wouldn't be well suited to this application. That said though, you can get the additional switch socket adapter which would allow you to control any pump via the osmolator system. That way you can use a pump that can handle the head pressure.

Hello,
Just wondering if I need 2 ATO. I know you can place it either in the sump or in the tank, but my question is if I place it in the sump will it also refill my tank in that process. I don't see that happening but if it does please let me know.

Bulk Reef Supply
Hi Ronald,
If you have a sump, it MUST go in the sump, in the chamber where your return pump is. This is the only area of your tank that will have a changing water level depending on evaporation (unless its far too late!). Only one ATO would be necessary but it must go in that location if you have a sump.

If i have a wave maker and this ATO in the same tank (I don't have a sump), would the waves cause the pump to turn on and off constantly? Thanks

Bulk Reef Supply
Hi Christian,
In theory it could present a problem but the circuitry in the Osmolator should help to prevent that. Every time the ATO is triggered it runs for a minimum of 15 seconds. It adds overfill to prevent short cycling. In most cases this should be sufficient unless the height of your waves is constantly changing.

Does the pump get placed directly in the top off water reservoir? If so what are the dimensions of that pump? I am trying to decide what kind of reservoir I can use before purchasing a ATO.

Bulk Reef Supply
Hey Mark,
That is correct. Its a submersible pump that gets stuck right into the top off water. If your interested in this ATO system you should give this blog article a quick read. It goes into a lot more detail on the system (which is one of my favorites).

My Tunze Osmolator ATO keeps getting stuck in the ON position. I soaked the electronic eye in vinegar and it was fine for a week, but then it stuck on again. Do these electronic eyes fail after many years of use? I've been using it for about 4 years. Is there any way to replace the eye without having to buy a whole new system?

Thanks,
Daire Fontaine

Bulk Reef Supply
Hi Daire,
We run into very few issues with these but after that length of time I would imagine its possible for any component to fail. We don't have individual parts like the optical eye, but if you give Roger and company a shout over at Tunze USA, he might. At the very least he could likely help you narrow down exactly what it is. The number I have for them is 512-833-7546 tunze@sbcglobal.net

Bulk Reef Supply tried many different water level switches and auto top off solutions before giving the Tunze 3155 Osmolater Universal Auto Top Off BRS Recommended status. Despite its higher price this is by far our favorite solution. Spending the extra money on a Tunze Osmolater will give you that extra peace of mind and insurance from having a disaster that ruins carpets or hard wood floors.

I have a litermeter 3 that has failed. It pushes water about 30 feet from the litermeter to a sump tank. Will this pump do the same?

Bulk Reef Supply
Hi Spencer,
The max head pressure on the included pump is about 7ft. It likely wouldn't be well suited to this application. That said though, you can get the additional switch socket adapter which would allow you to control any pump via the osmolator system. That way you can use a pump that can handle the head pressure.

Hello,
Just wondering if I need 2 ATO. I know you can place it either in the sump or in the tank, but my question is if I place it in the sump will it also refill my tank in that process. I don't see that happening but if it does please let me know.

Bulk Reef Supply
Hi Ronald,
If you have a sump, it MUST go in the sump, in the chamber where your return pump is. This is the only area of your tank that will have a changing water level depending on evaporation (unless its far too late!). Only one ATO would be necessary but it must go in that location if you have a sump.

If i have a wave maker and this ATO in the same tank (I don't have a sump), would the waves cause the pump to turn on and off constantly? Thanks

Bulk Reef Supply
Hi Christian,
In theory it could present a problem but the circuitry in the Osmolator should help to prevent that. Every time the ATO is triggered it runs for a minimum of 15 seconds. It adds overfill to prevent short cycling. In most cases this should be sufficient unless the height of your waves is constantly changing.

Does the pump get placed directly in the top off water reservoir? If so what are the dimensions of that pump? I am trying to decide what kind of reservoir I can use before purchasing a ATO.

Bulk Reef Supply
Hey Mark,
That is correct. Its a submersible pump that gets stuck right into the top off water. If your interested in this ATO system you should give this blog article a quick read. It goes into a lot more detail on the system (which is one of my favorites).

My Tunze Osmolator ATO keeps getting stuck in the ON position. I soaked the electronic eye in vinegar and it was fine for a week, but then it stuck on again. Do these electronic eyes fail after many years of use? I've been using it for about 4 years. Is there any way to replace the eye without having to buy a whole new system?

Thanks,
Daire Fontaine

Bulk Reef Supply
Hi Daire,
We run into very few issues with these but after that length of time I would imagine its possible for any component to fail. We don't have individual parts like the optical eye, but if you give Roger and company a shout over at Tunze USA, he might. At the very least he could likely help you narrow down exactly what it is. The number I have for them is 512-833-7546 tunze@sbcglobal.net

Full Details

Bulk Reef Supply tried many different water level switches and auto top off solutions before giving the Tunze 3155 Osmolater Universal Auto Top Off BRS Recommended status. Despite its higher price this is by far our favorite solution. Spending the extra money on a Tunze Osmolater will give you that extra peace of mind and insurance from having a disaster that ruins carpets or hard wood floors.

Reviews

Easy to use and no need to worry about your tankBy Hamadon 2/28/2015

It saved my time and i do not need to manualy add water. i used it for 200 gallon tank. Thanks BRS

Super ProductBy RDMon 2/20/2015

RDM would recommend this product to a friend

This was easy to setup and get working. I never realized how much I hated having to manually top off my water until I put this in my system. Now I just check my water levels and the fresh water supply and this takes care of adding water as and when it's needed.

EASY and works greatBy Jeffreyon 2/15/2015

Jeffrey would recommend this product to a friend

So far so good ! Have this set up on roughneck bin I'm using to cure my dry rock in. Works perfect and secondary safety offers great piece of mind. In the room one day when pump came on.. manually lifted float and audible alarm sounded and pump shut off. Very comforting to have a piece of equipment like this that is looking out for me ! If you are on the fence, JUST GET IT, you won't be disappointed.

fantastic ATOBy Hawrasseron 2/11/2015

Hawrasser would recommend this product to a friend

this ATO is great. keeps the water level in my sump constant. the only thing i would change is to make the amount of travel on the floating switch a little bit larger. if i turn on my protein skimmer it will sound the alarm but my skimmer is also huge haha

Hoping to get it workingBy Andrewon 1/16/2015

Andrew would recommend this product to a friend

I have had this on an AIO tank (40 gallon) worked great the first week, now it keeps overfilling my tank( alarm going off) in the process of troubleshooting it with Tunze, hope i can get it to work correctly. I wish it worked right out of the box, but based on reviews the Tunze auto top off is suppose to be the best. I have owned other Tunze products before with no problems. Not bashing the auto top off but its not working out of the box. But Tunze customer service is great at helping.

Great ATO! Never missed the target!By Alecon 1/15/2015

Alec would recommend this product to a friend

I don't need to add anymore to those 200+ reviews but I put mine on a timer that only turned on once a day for 10 mins. That way it's not pumping all day long and will never over fill.

Works Great By John Bon 1/10/2015

John B would recommend this product to a friend

Easy set up and I love the optical sensor. My old ATO float valve would often not register the water level depleting and I'd have to refill the sump manually. No issues so far and don't anticipate any. I did have to run the top off line into the tank overflow since my storage container is taller than the sump, but there was plenty of supply hose and I actually like it better.

Best ATO ever By Seadog09 on 1/7/2015

Seadog09 would recommend this product to a friend

The name alone represent quality so you know from start to finish that's what you'll get. I'm happy with my purchase and I know you will be too..

Works flawlessly.By DivingTheWorldon 1/5/2015

DivingTheWorld would recommend this product to a friend

I've had this running for about 4 months now and it works flawlessly. It's really a set it and forget it product. The one quirky thing is that when it first turns on, it will pump water for a few seconds to purge the pump of any air. This is normal and not a but per say, but something to be aware of. I initially had this programmed on my Apex to only turn on a few times a day, but found that it was pumping too much water (due to the starting purge). So now I just leave it on 24 hours a day and it works fine.

Works as promisedBy Jay B.on 1/4/2015

Jay B. would recommend this product to a friend

I bought this to regulate the level in my sump, using RO/DI feed. I also purchased the optional valve. The setup is easy, especially because of the way that the two level sensors are cleverly mounted with the magnetic holder. I turned the water feed on on and everything worked like it was supposed to. Now I don't have to keep fiddling with my protein skimmer to get the right quantity skimmate.

Almost perfectBy Jimon 12/27/2014

Jim would recommend this product to a friend

This is a really great ATO system. There is one downside. If you are pumping the water into your sump, the top level of the top off water container supply cannot be higher than the sump water level. The pump is centrifical, and allows water to flow through the pump when it is off. If the top off water is higher than the sump water, a siphon will occur, and water will continue to flow until the water levels equalize (including over-running the sump, and onto the floor. You simply need to select the right top off container.

ATO's Don't Get Better Than This!By Bernieon 12/20/2014

Bernie would recommend this product to a friend

The Tunze was superior to my first ATO set up which used a float valve and lifter pump. The optical sensor is great and having the second float valve to protect against overfilling is just a smart investment to protect not only your tank but the flooring around it.

I have a controller in which I could probably have set something up myself but for an all in one package this system is great.

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